1. Field of the Invention
The invention is directed to a spring device at a swivelable hatch of a motor vehicle.
2. Description of the Related Art
In DE 36 00 845 A1, for example, a spring device of the type mentioned above is provided at a rear hatch of a motor vehicle and has a gas spring and a preloaded helper spring between the body of the motor vehicle and the rear hatch. The work stroke of the gas spring is selected in such a way that when closing the opened rear hatch the gas spring reaches its fully retracted position before the rear hatch is closed. The preloading of the helper spring is selected in such a way that it is greater than or equal to the ejection force of the fully retracted gas spring. After the gas spring has reached its fully retracted position and has come into contact with the preloaded helper spring, the helper spring is further compressed as the rear hatch is closed further until the helper spring reaches a middle length measurement. This has the advantage, e.g., when driving over bumps, that the gas spring does not carry out movements which impair stability. Possible elastic deformations of the body of the motor vehicle or of the rear hatch are compensated for by the compressed helper spring. After unlocking a lock of the rear hatch, the gas spring and the helper spring cause the rear hatch to open until reaching a pre-closing position which is close to the closed position and in which the helper spring has reached its maximum length which is defined by a stop. Subsequently, only the gas spring causes a complete opening of the rear hatch or assists in manual opening of the rear hatch. In this spring device, the preloading force of the helper spring substantially exceeds the gas force of the completely retracted gas spring so that a manual closing of the rear hatch is difficult or not readily possible. Therefore, additional, force-actuated locking elements are provided that enable a force-actuated closing of the rear hatch from the pre-closing position to the closed position and, to this end, require closing the rear hatch in several stages. Further, the force-actuated locking elements considerably increase the manufacturing effort and cost of the spring device.